A circuit board comprises a dielectric of sheet or card form on which is provided a pattern of electrical circuit path conductors, useful to interconnect electronic circuit components mounted on the card. The conductors are formed by a number of processes available from the prior art.
In one process, metal strips are cut out to desired shapes and then secured on the dielectric, using adhesives, fasteners or tab in slot joints. This process is not suitable for repeated, mass production.
According to another process, a metal laminate is provided over the dielectric and then coated with an etchant resist material that decomposes when exposed to light of particular wavelength. Prior to being exposed, the resist is shielded by a cover comprising a pattern of opaque circuit paths. The decomposed resist material is washed away leaving a pattern of resist material which was shielded by the cover. Then the metal layer is removed by an etchant except, for that which is covered by the pattern of resist material.
In another process, the dielectric normally resists application of metal by electroplating. However, the surface of the dielectric is treated to become sensitized to electroplating of copper. The metal is electroplated on selected areas of the dielectric to form a direct pattern of circuit paths. Alternatively, the electroplating may be applied, then selectively etched to form the circuit paths.
Those processes which involve etching or electroplating are accurate and repeatable, and thus are suited for mass producing circuit boards. However these processes are costly, since they require chemical solutions which need replenishment and waste treatment. Many process steps are required, greatly increasing the opportunities for causing defects in the circuits. Densely spaced, narrow circuit paths are difficult to produce. The spacing between circuit paths add up to a large nonutilized area which limits miniaturization of the circuit board.